title: "Affect of anaerobiosis on the antibiotic susceptibility of H. influenzae".
abstract: BACKGROUND
  Haemophilus influenzae is a human-restricted facultative anaerobe which resides mostly in the oropharynx. The majority of isolates recovered from the throat are unencapsulated commensals (NTHi), but depending on host susceptibility they cause bronchitis, otitis media and on occasion bacteremia and meningitis. Because of the variable oxygen availability in the various niche permitting bacterium replication, the organism must thrive in well oxygenated surfaces, such as pharyngeal epithelium to anoxic environments like the bottom of a Biofilm and in airway mucus. Other reports indicate that H. influenzae use aerobic respiration, anaerobic respiration and fermentation to generate ATP. To gain insight in to the activity of several classes of antibiotics against five well-characterized unencapsulated H. influenzae in room air, in 5% CO2 and under strict anaerobiosis. We also tested for the role of oxidative killing by all cidal antibiotics.
  
  
  RESULTS
  In comparison to room air, testing in 5% CO2 had minimal effects on the susceptibility to aminoglycosides, cephalosporins, tetracycline and chloramphenicol: the MIC of rifampin and ciprofloxacin increased eight fold with certain strains in 5% CO2. All antibiotics, except trimethoprim were cidal under both growth conditions. Aminoglycosides remained bactericidal in a strict anaerobic environment, while a reliable MBC was obtained with trimethoprim only under anaerobic conditions. Kinetic analysis of the cidal action of spectinomycin and tetracycline indicated slower killing anaerobically. An oxidative mechanism for aerobic killing could not be demonstrated.
  
  
  CONCLUSIONS
  We conclude that β-lactams, cephalosporins, macrolides, tetracycline's, aminoglycosides, chloramphenicol, rifampin and ciprofloxacin are bactericidal against five well-characterizes H. influenzae in an aerobic and anaerobic environment. The activity of trimethoprim was increased in anaerobic conditions.
authors.affiliation: Center for Childhood Infections, Seattle Children' Research Institute, 1900 Ninth Ave Seattle, Seattle, WA 98101, USA.
authors.forename: Hannah Kendall
authors.initials: HK
authors.lastname: Smith
authors.forename: Kevin Lee
authors.initials: KL
authors.lastname: Nelson
authors.forename: Edison S
authors.initials: ES
authors.lastname: Calaunan
authors.forename: Arnold Lee
authors.initials: AL
authors.lastname: Smith
authors.forename: Victoria
authors.initials: V
authors.lastname: Nguyen
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002463:Cell Membrane Permeability; D006193:Haemophilus influenzae / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D018384:Oxidative Stress
chemical_list: D000900:Anti-Bacterial Agents